The present invention relates in general terms to light emitting apparatus for a motor vehicle. Such apparatus typically comprises external indicating lights or signal lights, normally mounted on the outside of the vehicle; but it may also consist, for example, of lights for giving internal illumination, or warning lights for the driver of the vehicle.
A motor vehicle indicating light conventionally comprises a light source, which is typically the filament of an incandescent lamp, together with optical means which are arranged to propagate the light flux which is emitted by the source in such a way as to satisfy a photometric grid laid down by regulations. In this type of indicating function, this grid is of a minimum size, which is well defined both in height and in width, and the light must be distributed essentially homogeneously within this grid.
In order to attain these objectives, it is usual practice to include in the optical means a flux recuperator such as a Fresnel lens or a parabolic reflector which is focused on the light source, together with means for diffusing the light by refraction, which typically take the form of motifs which are in general arranged on the internal surface of the front optic, or cover lens, of the indicating light. Such motifs may for example consist of striations or spherical or toroidal projecting elements.
The said optical means fulfil the required functions as far as the traffic or vehicle lighting regulations are concerned, but they do in general give the indicating light an irregular appearance when it is extinguished and seen from outside. In addition, it will easily be understood that they call for a particularly large amount of design work and theoretical study of the photometry in order to manufacture the mould in which the optical element concerned is to be made.
In this connection, techniques are known that are intended to improve, firstly the homogeneity of the beam produced by an illuminating or indicating device, and secondly its appearance when extinguished. One of these techniques consists in frosting the surface of the flux recuperating reflector associated with the lamp, and/or the optic or cover glass of the apparatus. In particular, when such frosting is effected on the outer face of an optic, it masks, to some degree, the refracting reliefs formed on its internal face.
Such frosting does however have the disadvantage that it makes it necessary to do additional work on the component concerned, which is detrimental to the eventual cost of the apparatus as a whole. In addition, when the internal face of an indicating light optic is frosted in this way, the frosting may become changed, for example by abrasion in the mould, or due to wear in the mould so that the amount of frosting in the components produced in a long production run in the same mould will gradually deteriorate. Finally, the frosting is difficult to adjust precisely to the requirements of the indicating light in terms of photometry or homogeneity of appearance.
A main object of the present invention is to overcome the above mentioned drawbacks of the state of the art. More precisely, the present invention proposes first to make indicating lights having an external appearance when extinguished which is very homogeneous without any frosting, or depolishing, having to be carried out, treatment whatever, while at the same time considerably simplifying the form, and therefore the design and moulding, of the optical components which diffuse the light.
Accordingly, the present invention proposes a lighting and/or indicating apparatus for a motor vehicle, comprising a light source which cooperates with optical means for diffusing the light, characterised in that the light diffusing means comprise a plate through which the light issued from the light source can pass, the mass, that is to say the body, of the said plate being made of a transparent first material having a first refractive index and in which inclusions are embedded, the inclusions being of a transparent second material having a second refractive index different from the first.
The inclusions are preferably generally spherical. Their size is preferably in the range between about 0.1 xcexcm and 100 xcexcm. Preferably, the inclusions constitute between 0.05 and 5% of the weight of the plate.
According to a preferred feature of the invention the said first material is a polymethylmethacrylate, the second material being a copolymer of the polyacrylate family.
The two said materials may be uncolored, or the first material may be colored and the second uncolored, or they may both be colored.
Refracting reliefs may be formed on one of the faces of the plate. The plate may constitute a cover glass, or globe, or optic of the apparatus.
The apparatus may for example be an external indicating light or an internal illuminating light, or an indicating light for giving signals to the driver of the vehicle.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.